Conventionally, as the actinic energy radiation curable ink-jet ink, there are a radically polymerizable and a cationically polymerizable ink-jet inks. Further, of these, known are a non-solvent-type curable ink-jet ink containing substantially no solvent and a solvent dilution-type curable ink-jet ink of low viscosity positively diluted with water or solvent. Fundamentally, the actinic energy radiation curable ink-jet ink features quick drying performance. Therefore, there has widely been brought into practical use a non-solvent-type curable ink-jet ink requiring no solvent-drying load during ink-jet recording or a curable ink-jet ink with a slightly added solvent. Of these, the radically polymerizable ink-jet ink features a wide selection of materials, which, thereby, has great flexibility for ink designing and is widely being researched and developed, resulting in being put into practical use. In contrast, the cationically polymerizable ink-jet ink is unaffected by polymerization inhibition caused by oxygen, and thereby has such advantages that excellent small droplet curability and excellent curability with a low energy radiation source are expressed and a relatively highly flexible cured film can be obtained.
As a cationically polymerizable ink-jet ink composition, those, in which an oxetane compound, an alicyclic epoxy compound, or a vinyl ether compound is used as a polymerizable compound, are widely known (for example, refer to Patent Document 1).
In any of the ink-jet ink compositions disclosed therein, the added amount of an alicyclic epoxy compound is needed to increase to realize adequate curing sensitivity, which, thereby, has produced problems such as an increase in ink viscosity or a decrease in flexibility of a cured film. From the viewpoint of realizing ink viscosity reduction and flexibility of a cured film, a vinyl ether compound is a useful monomer due to its relatively low viscosity, as well as low glass transition point of a cured film. Therefore, actinic energy radiation curable ink-jet inks containing vinyl ethers are proposed and disclosed (for example, refer to Patent Documents 2-4).
In Patent Document 2, an ink-jet ink containing a vinyl ether compound having an average molecular weight 300 to 5,000 is disclosed in which a layer is highly curable and durable.
In Patent Document 3, an image forming method which performs curing with an LED light source is disclosed in which an ink-jet ink containing triethyleneglycol divinyl ether, a pigment, a dispersant, a diallyl phthalate prepolymer, a cationic polymerization initiator, and a sensitizer are used.
In Patent Document 4, a photo-curable resin composition comprising a propenyl ether compound as a kind of vinyl ether is disclosed and applications for a printing ink or a coating agent which has a good curability are proposed.
However obtained sensitivity of curability still did not reach to a sufficient level which the present inventor expected. Therefore the present inventor studied ink-jet ink compositions based on vinyl ether by arranging composition suitable to an activated energy radiation curable and low viscosity for ink-jet use using examples from Patent Documents. As the results, it is found that ink-jet inks based on vinyl ether has specific issues for an ink-jet recording method. For example, in some special recording condition cases in which an image is formed by a serial recording method using divided image and multi-scanning, new problems such as lowering curability specifically, lowering physical properties of layers and odor are occurred. As a result of such diligent investigations, it is found that these problems relate to curing property of inks ejected on an ink which is radiated by an activated energy radiation. This phenomenon markedly occurs when ink of small droplets or thin layer by ink-jet recording is cured with under high humid circumstances.
Other than vinyl ether, cationically polymerizable monomer such as oxcetan compound or epoxy compound or radical polymerizable monomer based on acrylate may be used in combination. However because vinyl ether itself has poor copolymerization with other monomers, it is difficult to obtain stable curing properties. Therefore heretofore an application of vinyl ether to an ink-jet recording method is compelled to restrict a range of use such as suppressing content or limiting curing condition or process.    [Patent Document 1] Japanese Patent Publication No. 3014251    [Patent Document 2] Unexamined Japanese Patent Application Publication (hereinafter referred to as JP-A) No. 2005-8758    [Patent Document 3] JP-A No. 2008-280460    [Patent Document 4] Japanese Patent Publication No. 2881134